Despite many advances in the treatment of cancer in recent years, most malignant tumors are currently incurable unless they are detected at an early stage. One approach to increasing the success of cancer therapy in this setting is to augment the ability of the body's immune defense system to destroy residual cancer cells after surgery, radiation or chemotherapy. A major component of the body's immune defense system is the major histocompatibility (MHC) Class I gene system also known as the human leukocyte antigen (HLA) Class I gene complex. Expression of the genes of the HLA Class I complex plays a critical role in the function of cell-mediated killing of tumor cells. Another approach which has allowed cure of previously incurable patients with hematologic malignancies is bone marrow transplantation. Tbe ability to utilize this treatment modality is also dependent on the type of HLA Class I gene expression in the bone marrow donor and recipient. The long term objectives of this project are to elucidate cell-type specific and allele-specific mechanisms responsible for the constitutive and immune interferon (IFNgamma) mediated regulation of HLA Class I gene expression in human hematopoietic tumor cells and lymphoid hematopoietic cells. The ultimate goal of these studies is to provide a rational basis for therapeutic manipulation of HLA Class I gene expression to facilitate host defense killing of tumor cells and to facilitate the ability to carry out bone marrow transplantation across MHC Class I barriers. Several specific questions will be addressed to achieve the long term objectives of this project: 1) What is the nature and specificity of a newly described constitutive control element in the 5' flanking region of the HLA-A2 I gene and the trans-acting nuclear protein that binds to this element? 2) What are the exact cis-acting sequences of a novel 3'interferon response element and corresponding nuclear protein binding complex present in the HLA-A2 gene, and is this element allele specific? These questions will be answered by functional analysis of the cis-acting regulatory sequences through in vitro mutagenesis and DNA-mediated gene transfer into human tumor and lymphoid cells. The trans-acting factors that mediate the effects of both the constitutive and interferon responsive regulatory sequences will be characterized by employing a combination of biochemical purification procedures as well as direct screening of cDNA expression libraries to obtain purified factors and the genes that encode them. These factors will then be analyzed functionally in biochemically defined in vitro transcription assays and by surrogate genetic techniques. The interactions between the constitutive and interferon responsive control elements of HLA Class I gene expression will be tested in DNA-mediated gene transfer genetic assays and in vitro biochemical assays. Besides the specific information related to the regulation of HLA Class I gene regulation in human tumor and lymphoid cells, which ultimately could have relatively direct clinical applications, it is anticipated that knowledge gained about the basic mechanisms controlling Class I gene expression could have broad application in understanding and manipulating this critical component of the human immune system.